1. Field of the Invention
The invention relates to a connector for fixing a flexible substrate thereon and connecting the flexible substrate to contacts assembled into the connector.
2. Description of the Related Art
Such a connector has been required to be able to connect a flexible substrate to contacts in a higher density, to be formed in a smaller size, and to have higher operability and reliability. For instance, Japanese Unexamined Patent Publication No. 9-82427 and Japanese Unexamined Utility Model Publication No. 6-77186 have suggested a connector for connecting a flexible substrate or flat cable to contacts.
FIGS. 1A to 1C are cross-sectional views of the connector suggested in Japanese Unexamined Patent Publication No. 9-82427, illustrating steps of inserting a flat cable thereto.
The illustrated connector 101 is comprised of a housing 102 which is upwardly open, a plurality of first contacts 103a assembled into the housing 102 from a front side (a right side in FIG. 1A) of the housing 102, a plurality of second contacts 103b assembled into the housing 102 from a rear side (a left side in FIG. 1A) of the housing 102, and a lever 108 rotatably supported above the housing 102.
As illustrated in FIG. 1A, each of the first contacts 103a has an extension 104a extending towards the rear side of the housing 102, a contact 106a formed on the extension 104a in the vicinity of a distal end thereof for making electrical contact with a flat cable 109 (see FIG. 1C), and a lead terminal portion 105a extending in an opposite direction to the extension 104a. As illustrated in FIG. 1B, each of the second contacts 103b has an extension 104b extending towards the front side of the housing 102, a contact 106b formed on the extension 104b at a distal end thereof for making electrical contact with the flat cable 109, a lead terminal portion 105b extending in an opposite direction to the extension 104b, and a support portion 107b extending towards the front side of the housing 102 above the extension 104b.
The lever 108 is carried at the support portion 107b for rotation. The lever 108 is designed to compress and thus fix the flat cable 109 onto the housing 102 at a certain rotation angle, as illustrated in FIG. 1C. Lines connecting a rotational center 110 of the lever 108 to both the contacts 106a and 106b make an isosceles triangle.
FIG. 2 illustrates the connector suggested in Japanese Unexamined Utility Model Publication No. 6-77186. The illustrated connector 201 is comprised of a housing 202 which is open upwardly, a plurality of contacts 203, and a lever 210 for compressing and fixing a flexible substrate 209 onto a later mentioned U-shaped contact member 205 of the contacts 203. Each of the contacts 203 has a support portion 204 for supporting the lever 210 for rotation, a U-shaped contact member 205 onto which the flexible substrate 209 is compressed, a contact 208 formed on the U-shaped contact member 205 at a distal end thereof, a lead terminal portion 206 for electrically connecting the flexible substrate 209 to an external element (not illustrated), and an arm portion 207 for connecting the support portion 204, the U-shaped contact member 205, and the lead terminal portion 206 together.
The contacts 203 are assembled into the housing 202 from a rear side (a left side in FIG. 2) of the housing 202. The lever 210 is designed to be rotatable about a tip end of the support portion 204 of the contacts 203. The lever 210 is formed with a raised portion 211, which is situated outside a line connecting a center of the tip end of the support portion 204 to the contact 208 of the contacts 203 when the lever 210 is in a position illustrated in FIG. 2, and situated inside the line when the lever 210 rotates to such a position that the flexible substrate 209 is compressed onto the U-shaped contact member 205 by the lever 210.
FIG. 3A is a graph showing a force exerted when the flat cable 109 is compressed onto the housing 102 by the lever 108 in the connector 101 illustrated in FIGS. 1A to 1C. Now, an angle formed between the lever 108 and the flexible substrate 109 is represented with ".theta.". FIG. 3A shows a relation between a force F exerted on the flexible substrate 109 by the lever 108 and an angle (90.degree.-.theta.).
An origin O of the graph shows that the angle .theta.is equal to 90 degrees, that is, the lever 108 stands upright, as illustrated in FIG. 1A. After the lever 108 starts rotation, the lever 108 makes contact with the flexible substrate 109 and begins compressing the flexible substrate 109 onto the housing 102 at the point A. Then, the force F gradually increases as the lever 108 rotates. The force F is maximized at the point B. FIG. 3B illustrates that the lever 108 makes the angle .theta. with the flexible substrate 109 and exerts the maximum force F.sub.max on the flexible substrate 109. Then, the force F gradually decreases as the lever 108 rotates, and finally becomes equal to F.sub.end at the point C when the lever 108 finishes rotation, as illustrated in FIG. 3C. A self-locking force S defined as a difference between the forces F.sub.max and F.sub.end keeps the flexible substrate 109 compressed by the lever 108.
The above-mentioned relation between the force F and the rotation angle .theta. of the lever 108 is established also in the connector illustrated in FIG. 2.
As mentioned above, the flexible cable 109 is compressed onto the housing 102 with the force F. However, the connector 101 is accompanied with a problem that the force F expected to be as high as possible for fixing the flexible cable 109 cannot be maximized when the lever 108 finishes rotation as illustrated in FIG. 3C. The same problem is paused in the connector 201 illustrated in FIG. 2.
The reason why such a problem is caused is as follows. As illustrated in FIG. 3A, the force F is maximized at the point B when the lever 108 is still rotating, and finally becomes equal to F.sub.end which is smaller than F.sub.max. The conventional connectors 101 and 201 are designed to fix the flexible substrate 109 and 209 with the contact force F, and exert the maximum contact force F.sub.max on the flexible substrates 109 and 209 when the levers 108 and 210 are still in rotation. Hence, suppose that a maximum force which the flexible substrate 109 and 209 allow to receive is equal to the maximum contact force F.sub.max, the force F.sub.end obtained when the levers 108 and 210 finish rotation thereof is smaller than the force F.sub.max. For this reason, the above-mentioned problem is paused.